Question 620620

hi, my quadratic equation is (x+5)(x+8) =126.75
ive got these steps with help from a friend but as i need to show my working this wont be enough, i struggle with quadratics, what stages am i missing here?

X^2 + 13X  –  86.75 =0
X=4.85782
X=4.85

thanks
Sam


You seem to have forgotten about the negative value of x. That's all!!


{{{x^2 + 13x - 86.75 = 0}}}, with a = 1; b = 13; and c = - 86.75


Using the quadratic equation{{{x = (-b +- sqrt( b^2-4*a*c ))/(2*a) }}}, we get:


{{{x = (- 13 +- sqrt( 13^2-4*1*-86.75 ))/(2*1) }}} ----- {{{x = (- 13 +- sqrt( 169 + 347))/2 }}} ------ {{{x = (- 13 +- sqrt(516))/2 }}} 


{{{x = (- 13 +- (22.71563338))/2 }}}


{{{x = (- 13 + 22.71563338)/2 }}}, or {{{x = (- 13 - 22.71563338)/2 }}}


{{{x = (9.71563338)/2 }}}, or {{{x = (- 35.71563338)/2 }}}


{{{highlight_green(x = 4.85781669)}}}, or {{{highlight_green(x = - 17.85781669)}}}


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